It passed emissions with flying colors! HC was cut in half and CO went from 50+ to 6 or so, and the limit is 12. Now I’m in line at DMV with 50 people ahead of me in the line, as expected.
I bought an odb2 reader and cleared the bad sensor code - just so my day isn’t completely perfect, a new code popped up - driver side oxygen sensor is bad as well :). This time, I’ll try removing the tire and removing it from the side with a long breaker bar. I hope it isn’t seized - but if it is, I have the manifold ready, new oxygen sensor on the way ($45 on amazon vs 80 at autozone) and now I know what I’m getting myself into.
Huge thank you to everyone that pitched in with ideas on what to do to pass the emissions. We replaced: passenger side exhaust manifold, oxygen sensor, gaskets, air filter, spark plugs, and I cleaned the mass airflow sensor with carburetor cleaner. It was probably a little bit of everything that helped. Original, 18 year old spark plugs looked like < instead of [ on one side, so they were probably not helping much.
I feel so accomplished doing this, sacrificing knuckle skin to engine gods, but making it work in the end.